Bladder stones in dogs form when minerals in urine clump together into solid crystals, then gradually grow into stones. The two most common types, calcium oxalate and struvite, account for roughly 80% of all cases. Each type has a different cause, from bacterial infections and genetic conditions to metabolic imbalances and diet.
How Bladder Stones Form
Urine naturally contains dissolved minerals. When those minerals become too concentrated, the urine is too acidic or too alkaline, or an infection changes the chemistry of the bladder, crystals begin to precipitate out of solution, much like sugar crystallizing at the bottom of a supersaturated drink. Once a tiny crystal seed forms, additional minerals layer on top of it over weeks or months until a visible stone develops. Some stones stay small as grains of sand. Others grow to fill much of the bladder.
Three conditions drive this process regardless of stone type: high mineral concentration in the urine, a urine pH that favors that particular mineral, and low urine volume (meaning the dog isn’t drinking enough or urinating frequently enough to flush minerals out). The specific mineral involved determines what kind of stone forms and what triggered the problem in the first place.
Struvite Stones and Urinary Infections
Struvite stones make up about 37% of bladder stones submitted for analysis in dogs, and they are almost always caused by a urinary tract infection. The bacteria responsible, most commonly Staphylococcus species, produce an enzyme called urease that breaks down urea in the urine. This chemical reaction releases ammonia, which makes the urine more alkaline. In that alkaline environment, magnesium, ammonium, and phosphate combine to form struvite crystals.
Because infection is the root cause, struvite stones are sometimes called “infection stones.” They can form relatively quickly once a UTI takes hold, and they tend to recur if the infection isn’t fully cleared. Female dogs are more prone to UTIs, which makes them more commonly affected by struvite stones than males. Prevention focuses on catching and treating urinary infections early, monitoring urine samples regularly, and in some cases feeding a therapeutic diet that keeps the urine slightly acidic and lower in protein, phosphorus, and magnesium.
Unlike most other stone types, struvite stones can often be dissolved without surgery. A combination of antibiotics to eliminate the infection and a special diet that acidifies the urine and reduces the building blocks of struvite can shrink these stones over several weeks. This only works for infection-induced struvite, which is the predominant form in dogs.
Calcium Oxalate Stones and Metabolism
Calcium oxalate is the single most common stone type in dogs, accounting for about 43% of analyzed stones. These stones form when excess calcium ends up in the urine, a condition called hypercalciuria. The calcium binds with oxalate, a natural byproduct of metabolism, and crystallizes in acidic urine (typically below a pH of 6.6).
The excess calcium in urine can come from several sources. Sometimes the gut absorbs too much calcium from food. Sometimes bone turnover releases calcium into the bloodstream faster than normal. In other cases the kidneys simply fail to reabsorb calcium efficiently. Often, no single clear cause is found. Diets that are high in sodium, protein, or acid-forming ingredients can also push more calcium into the urine. Overactive parathyroid glands and Cushing’s disease (hyperadrenocorticism) are known risk factors as well, though the exact mechanism for Cushing’s isn’t fully understood.
Calcium oxalate stones cannot be dissolved with diet or medication once they’ve formed. They need to be physically removed, either through surgery or a minimally invasive procedure. After removal, prevention relies on increasing water intake to keep urine dilute, feeding a diet that doesn’t overly acidify the urine, and addressing any underlying metabolic conditions contributing to high calcium levels.
Urate Stones and Liver Function
Urate stones account for about 4% of canine bladder stones overall, but they are dramatically overrepresented in certain breeds, especially Dalmatians. These stones form from uric acid, a waste product of purine metabolism. Concentrated urine and acidic urine are the two biggest drivers of urate crystallization.
Dalmatians carry a genetic mutation in a transporter gene called SLC2A9 that affects how the liver and kidneys handle uric acid. In most dogs, the liver converts uric acid into a more soluble compound that’s easy to excrete. Dalmatians can’t do this efficiently, so their urine contains far more uric acid than other breeds. Research measuring uric acid levels found that affected dogs had urine concentrations three to eight times higher than dogs without the mutation. Every Dalmatian carries two copies of this recessive mutation, making the entire breed predisposed.
Dogs with liver shunts, a condition where blood bypasses the liver through abnormal blood vessels, can also develop urate stones because their liver can’t properly process uric acid. Breeds prone to liver shunts, such as Yorkshire Terriers and Miniature Schnauzers, occasionally develop urate stones for this reason. Urate stones become more soluble at higher pH, so dietary management typically involves reducing purine intake (less organ meat and certain proteins) and sometimes using medication to lower uric acid production.
Cystine Stones and Genetic Defects
Cystine stones are uncommon, representing about 2% of stones in dogs, but they reveal a clear genetic pattern. Cystinuria is an inherited defect in which the kidneys fail to reabsorb cystine, a poorly soluble amino acid, from the urine. The same transporter defect also affects reabsorption of three other amino acids: ornithine, lysine, and arginine. When cystine accumulates in the urine and the pH is acidic, it crystallizes into stones.
Different breeds carry different mutations, and researchers have classified canine cystinuria into several types. Newfoundlands and Labradors carry mutations in the SLC3A1 gene that cause a severe, early-onset form. Australian Cattle Dogs have a different deletion in the same gene. Miniature Pinschers carry a mutation in a different gene entirely, SLC7A9. A third type, seen in Mastiffs, English and French Bulldogs, Basset Hounds, and Irish Terriers, depends on male hormones and occurs only in intact males, typically appearing later in life. English Bulldogs and Mastiffs carry some of the highest risk among all breeds, with odds ratios of 44 and 53 times the baseline risk, respectively.
Because cystine is more soluble in alkaline urine, management focuses on making the urine less acidic and keeping it dilute. In hormone-dependent forms, neutering can reduce or eliminate stone recurrence.
Less Common Stone Types
Silica stones are rare, making up less than 1% of cases, but dietary factors appear to play a role in their formation. Dogs eating diets high in plant-based ingredients like corn gluten or grain hulls may be at increased risk, though the exact mechanism isn’t well established. Xanthine stones are even rarer and can occur as a side effect of medication used to treat urate stones, or from an inherited enzyme deficiency.
Risk Factors That Apply to All Stone Types
Regardless of the mineral involved, several factors increase the overall likelihood of bladder stone formation. Low water intake is one of the most important. When dogs drink less, their urine becomes more concentrated, giving dissolved minerals a better chance to crystallize. Encouraging water consumption by feeding canned food, adding water to dry kibble, or providing multiple fresh water sources helps dilute the urine and flush crystals before they can grow into stones.
Breed matters significantly. Beyond the genetic conditions already mentioned, smaller breeds like Miniature Schnauzers, Shih Tzus, Bichon Frises, and Lhasa Apsos are frequently diagnosed with calcium oxalate stones. Diet composition influences urine pH and mineral content directly. Diets that heavily acidify urine push dogs toward calcium oxalate, while persistent alkaline urine (especially from infection) favors struvite. Feeding patterns also matter: infrequent meals can cause wider swings in urine pH throughout the day, potentially creating windows where crystallization is more likely.
How Bladder Stones Are Found
Most bladder stones show up on a standard X-ray. In one study of 202 dogs, 98% of stones were visible on radiographs. Calcium oxalate stones are consistently radiopaque and visible every time. Struvite stones are usually visible too, though about 7% were radiolucent and didn’t show up on X-rays. Cystine stones, historically considered hard to see on imaging, were visible 97% of the time in the same study.
When X-rays are inconclusive, ultrasound reliably detects stones regardless of mineral type. Urine analysis provides additional clues: the pH, the presence of crystals, and whether bacteria are growing all help narrow down the stone type before removal. The only way to confirm composition with certainty, though, is to send a removed stone to a laboratory for mineral analysis. Knowing the exact type is critical because it determines whether the underlying cause is an infection, a metabolic disorder, or a genetic condition, and each requires a completely different prevention strategy.